Disease relevance of NARS

• Human cytosolic asparaginyl-tRNA synthetase: cDNA sequence, functional expression in Escherichia coli and characterization as human autoantigen [1].
• Histidyl-tRNA synthetase and asparaginyl-tRNA synthetase, autoantigens in myositis, activate chemokine receptors on T lymphocytes and immature dendritic cells [2].
• These observations represent direct evidence that potent hASNS inhibitors may prove to be effective agents for the clinical treatment of acute lymphoblastic leukemia [3].
• In Brugia malayi, the gene for asparaginyl-tRNA synthetase (AsnRS), a class II AARS, previously has been identified as a multicopy gene encoding an immunodominant antigen in the serum of humans with lymphatic filariasis [4].

High impact information on NARS

• Asparaginyl-tRNA synthetase induced migration of lymphocytes, activated monocytes, iDCs, and CCR3-transfected HEK-293 cells [2].
• To test the possible involvement of Asn-tRNAAsn in regulating the levels of asparagine synthetase, we have examined the levels of asparagine synthetase in a mutant of CHO cells containing a temperature-sensitive asparaginyl-tRNA synthetase [L-asparagine:tRNA ligase (AMP-forming), EC 6.1.1.22] [5].
• Interspecific cell hybrids between human leukocytes and temperature-sensitive Chinese hamster cell mutants with either a thermolabile leucyl-tRNA synthetase or a thermolabile asparaginyl-tRNA synthetase were used as the starting material in these experiments [6].
• Asparaginyl-tRNA (Asn-tRNA) is generated in nature via two alternate routes, either direct acylation of tRNA with asparagine by asparaginyl-tRNA synthetase (AsnRS) or in a two-step pathway that requires misacylated Asp-tRNA(Asn) as an intermediate [7].
• The canonical ortholog for AsnRS is absent from most archaebacterial and some eubacterial genomes, indicating that in those organisms, formation of asparaginyl-tRNA is independent of the enzyme [8].

Biological context of NARS

• A bacterial extract containing the fusion protein catalyzed the aminoacylation reaction of S.cerevisiae tRNA with [14C]asparagine at a 20-fold efficiency level above the control value confirming that this cDNA encodes a human AsnRS [1].
• Isolation and characterization of interspecific heat-resistant hybrids between a temperature-sensitive chinese hamster cell asparaginyl-tRNA synthetase mutant and normal human leukocytes: assignment of human asnS gene to chromosome 18 [9].
• While the mechanism by which asparaginyl-tRNA synthetase affects cell-cycle progression has not been elucidated, it can be shown that it is not mediated through alteration in overall levels of protein synthesis [10].
• Drug resistance in lymphoblastic and myeloblastic leukemia cells is poorly understood, with several lines of evidence suggesting that resistance can be correlated with upregulation of human asparagine synthetase (hASNS) expression, although this hypothesis is controversial [3].
• Recombinant B. malayi AsnRS was used to perform cellular function assays--for example, chemotaxis and kinase activation assays.Results [11].

Anatomical context of NARS

• We isolated interspecific somatic cell hybrids between human peripheral leukocytes and a temperature-sensitive CHO cell line with a thermolabile asparaginyl-tRNA synthetase [9].
• In vitro heat-inactivation profiles of cell-free extracts from temperature-resistant hybrid cells indicate the presence of two forms of asparaginyl-tRNA synthetase [9].
• Unlike human AsnRS, parasite AsnRS is chemotactic for neutrophils and eosinophils [11].
• In situ hybridization using a B. malayi AsnRS-specific oligonucleotide probe identified abundant cytoplasmic mRNA, particularly in the hypodermis of adult B. malayi [4].
• Polyclonal antibody raised against recombinant human AsnRS identified abundant antigenic material in the pancreas, in particular in islet cells [12].

Associations of NARS with chemical compounds

• In other bacteria, particularly those that lack AsnRS, AspRS is nondiscriminating (ND-AspRS) and generates both Asp-tRNA(Asp) and the noncanonical, misacylated Asp-tRNA(Asn); this misacylated tRNA is subsequently repaired by the glutamine-dependent Asp-tRNA(Asn)/Glu-tRNA(Gln) amidotransferase (Asp/Glu-Adt) [13].
• Analogs of one of these classes of inhibitors, the long side-chain variolins, cannot bind to the adenosyl pocket of the closed conformation of AsnRS due to steric clashes, though the short side-chain variolins identified by SLIDE apparently bind isosterically with adenosine [14].
• In the absence of tRNA, AsnRS synthesizes diadenosine triphosphate, a potent regulator of cell growth in other eukaryotes [4].
• The anomalous dispersion of a uranium derivative of asparaginyl-tRNA synthetase (hexagonal, a = 124.4 A, c = 123.4 A) has been measured at three wavelengths near the M(V) edge using beamline ID1 of the ESRF [15].
• [3H]Asparagine was incorporated into protein by mitochondria of the Chinese hamster ovary (CHO) cell line Asn-7, which has a temperature-sensitive cytosolic asparaginyl-tRNA synthetase, either in the presence of cycloheximide or at a nonpermissive temperature [16].

Regulatory relationships of NARS

• In corroboration with these results it was shown that a different temperature-sensitive asparaginyl-tRNA synthetase mutant isolated in another laboratory was blocked in S phase in a manner similar to that of ts24 [10].

Other interactions of NARS

• The relative level of AsnRS transcribed in adult female B. malayi was compared to the levels of a low abundance and medium abundance AARS by quantitative real-time RT-PCR [4].
• Mutants having low activity for MetRS, AsnRS, or GlnRS contained aaRSs that were inactivated much more rapidly upon heating than those from wild-type cells [17].
• Under conditions of limited asparaginyl-tRNA synthetase activity in the mutant, there is a 2- to 3-fold increase in the level of asparagine synthetase activity [5].
• A temperature-sensitive mutation in asparaginyl-tRNA synthetase causes cell-cycle arrest in early S phase [10].
• The simulations are analyzed to determine the interactions that Asn is able to make in the binding pocket, and which sequence differences between AspRS and the highly homologous AsnRS are important for modifying the amino acid specificity [18].

Analytical, diagnostic and therapeutic context of NARS

• The affinity chromatography purified fusion protein efficiently aminoacylated unfractionated calf liver and yeast tRNA but not E.coli tRNA, suggesting that the recombinant protein is the cytosolic AsnRS [1].
• Human asparaginyl-tRNA synthetase: molecular cloning and the inference of the evolutionary history of Asx-tRNA synthetase family [8].

References